Add a factor level to a table

I have built a contingency table from a column in a dataframe:

> dat <- data.frame(x = c(1, 1, 3))
> table(dat)
x
1 3 
2 1

I want to add a "column" to the table for the missing factor levels (in this case "2") with a count of 0. The result should look like this:

> table(dat)
x
1 2 3 
2 0 1

I have searched the site and found many similar questions, but while they use the term "table" in the question title and body, they all actually ask about dataframes.

>Solution :

You need to explicitly specify the levels, i.e.

table(factor(dat$x, levels = 1:3))

# 1 2 3
# 2 0 1